Hydrogen sulphide is a highly toxic and corrosive environmental pollutant with an obnoxious smell which needs to be removed for pollution control as well as process requirements in industries. Natural gas processing complexes, refineries, sulphur processing chemicals industries, pharmaceutical industries, sugar industries, sewage treatment plants and bio-gas generating units are some of the major industries which need an economically viable solution for H2S removal and its safe disposal.
A number of processes have been known and are in commercial use for removing hydrogen sulphide from gas streams. However, these processes have some inherent limitations. The processes used for removal of H2S and there disadvantages are described in detail hereafter. Claus process is used for removing hydrogen sulphide from gases containing typically high concentration of H2S (more than 20% by vol of H2S). Liquid Redox process is used for removing hydrogen sulphide from gases containing typically low concentration of H2S.
Both the aforesaid process have the disadvantages of high capital and operating cost. Processes using iron sponges as catalyst have been in use wherein iron oxide deposited on wood shaving is used for removing hydrogen sulphide from gases. The major disadvantage with such a catalyst that these can be used as only once-through catalyst i.e. the catalyst after being used for removal of H2S can not be regenerated and hence has to be disposed as waste. Therefore, the cost of such treatment is high due to the use of stoichiometric quantities of chemicals and also disposal of the used materials.
Further, loading capacity i.e. the extent upto which the wood shavings can be loaded with the iron oxide is low, due to which, the hydrogen sulphide removal capacity in a single pass is limited. Also, safe disposal of the used catalyst is major problem.
In yet another process for hydrogen sulphide removal, a hot zinc oxide bed is used.
Zinc oxide is costlier than iron oxide. Another limitation of the process is that the bed gets exhausted after treating stoichiometric quanity of hydrogen sulphide once through the bed. The need of higher temperature for effective removal is another disadvantage as the gas needs to be preheated prior to treatment. Zinc oxide gets converted to zinc sulphide which is disposed off after the bed gets exhausted.
From the above descriptions of prior art, it is clear that there is a need for a more economical and simple process for hydrogen sulphide removal and its conversion to elemental sulphur using a solid bed incorporating inexpensive chemicals which can be regenerated and reused multiple times. This is the main objective of the present invention.